Привязка к вычисляемому свойству BindableProperty из кода ⇐ C#

[Гость]

In short, I have a custom control in Xamarin for which I defined a BindableProperty, which I would like to bind to the control's xaml via a calculated property in the code behind, but it always displays as null because the calculated property is evaluated when the BindableProperty didn't have a value yet, and afterward I am missing property changed notification logic. Which is the right way to do it?
Long explanation for context:
I am writing a custom control in Xamarin (which I named

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TabbedLayout

). I intend to bind an array of Views to a BindableProperty of the control, like so:

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To that effect I have defined a BindableProperty in the code behind the Control (TabbedLayout.xaml.cs):

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public static readonly BindableProperty TabContentsProperty = BindableProperty.Create(
nameof(TabContents),
typeof(View[]),
typeof(TabbedLayout),
null,
BindingMode.OneWay);

public View[] TabContents
{
get => (View[])GetValue(TabContentsProperty);
set => SetValue(TabContentsProperty, value);
}

However, from the control's xaml I wish to display only one of those Views. I have first defined a int property to control which is the selected index (with other parts of the control, let's assume that

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int SelectedIndex = 0

and I wish to display the first element).
I have then created a calculated property like so:

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public View DisplayedElement = TabContents?.ElementAt(SelectedIndex);

And I have bonded to it from the control's xaml like so:

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At this point, the ContentView displays empty because TabContents is still null.
From here, how would I update the view as soon as the BindableProperty value is set, the first time and every time it might be modified, to trigger a refresh of the bound DisplayedElement property?


Источник: https://stackoverflow.com/questions/781 ... ode-behind